Spark plug and method of manufacture therefor



R. J, L. DUTTERER SPARK PLUG AND METHOD OF MANUFACTURE THEREFOR Filed Feb. 14, 1947 INVENTOR. 21 e/TA. fiuf/e/e/ flffa/wza Patented Apr. 14, 1953 SPARK. PLUG AND METHOD OF MANUFACTURE THEREFOR J. L. Dutterer, Hastings, Mich, assignor to Hastings Manufacturing Company, Hastings;-

Mich;

Application February" 14, 19 17,- Serial No. 7281421 The inventionrelates to improvements in a spark plug and method of manufacture therefor.

The principal objects of this invention are:

First, to provide a spark plug for an internal combustion engine having improved operating characteristics.

Second, to provide a spark plug for an internal combustion engine having" accurately con" trollable' operating characteristics.

Third, to provide a spark plug which permits the operating characteristics of the plug to be accurately determined by a fluoroscopic or radiographic inspection.

Fourth, to provide a method of manufacturing spark plugs which reduces the cost of the spark plug by reducing waste and the number of faulty spark plugs produced.

Fifth, to provide a method for manufacturing spark plugs by means of which a uniform standard of operating characteristics can be assured throughout a. series of spark plugs.

Sixth, to provide a method for manufacturing spark plugs which permits a rapid and thorough inspection of the spark plug to determine the quality of its construction prior to the release of the plug for sale and distribution.

Seventh, to provide amethod of manufacturingspark plugs which permits the salvage and reclamation of faulty spark plugs.

Other objects and advantages pertaining to the details and economies of theinvention will be apparent from the following description and claims.

The drawings, of which there is one sheet, illustrate a preferred form of spark plug; and a view representing a fluoroscopic inspection step followed in the manufacture thereof.

Fig. 1 is an elevational view of my spark plug.

Fig. 2 is a vertical longitudinal cross sectional view through the insulator and center electrode of my spark plug.

Fig. 3 is an enlarged fragmentary vertical cross sectional view similar to Fig. 2 but illustrating in greater detail the connection and seal between the insulator and the center electrode.

Fig. 4; is a fragmentary view representing a. fluoroscopic view of a spark plug manufactured according to my method of manufacture.

It has long been recognized that the operating characteristics of spark plugs for internal combustion engines were dependent largely upon the type and quality of the seal between the center electrode and the insulator of the spark plug. The seal performs two functions of vital importance to the efficiencyof the spark plug, the first being to physically seal the center bore of the insulator against the escape of gases of the combustion chamber and the second being to form a heat transfer path from the center electrode to the walls of the insulator from where the heat can be dissipated to the shell of the spark plug. The later function is of particular importance because if insufficient heat is transferred from the electrode to the insulator, the center electrode will over-heat causing pro-ignition in the combustion chamber and if too large an amount of heat is dissipated from the center electrode the electrode will be relatively cold permitting partially burned oil and fuel in the combustion chamber to collect thereon and soon foul the plug so that it will not operate.

Various attempts have been made to control this later characteristic of spark plugs by designing the physical size of the center electrode and its area of contact with the insulator which, to a certain extent, controls the amount of heat which will be dissipated from the electrode. It has also been proposed to form the seal around the center electrode with a cement of powdered material having metal intermixed therewith to increase the heat conducting properties of the spark plug.

My invention provides a spark plug which not only has the desired heat conducting properties but one in which the rate of heat dissipation from the center electrode can be accurately controlled to a predetermined standard and which permits rapid and inexpensive inspection of each plug to-assure its conformity to the desired standard. As illustrated in the drawings my plug is of generally standard exterior appearance having a central insulator I mounted within a metal lic sleeve 2. The sleeve is provided with the usual threaded portion 3 and external electrode 4 and a terminal tip 5 is provided on top of the insulator for attaching the spark plug to the ignition system of the engine.

As illustrated in Fig. 2 the insulator i is provided with an external tapered shoulder 6 arranged to be engaged by the shell 2 and defines a central bore 1 which is internally threaded as at 8 and shouldered as at 9. The center electrode consists of an upper section 10 having threads ll formed on the lower end thereof and arranged to engage the threaded portion 8 of the central bore. A collar 12 is formed around the upper end of the upper section and arranged to engage the upper end of the insulator I to limit the distance the upper section may be screwed into the insulator.

The lower section of the electrode indicated at I3 projects downwardly through the lower end of the central bore and is provided with a tapered collar or flange M which seats against the shoulder in the central bore of the insulator. A cylindrical guide portion l5 extends upwardly above the collar 14 and serves to center a coil spring 16 within the central bore of the insulator. Attention is called to the fact that a recess of substantial length indicated at H is formed by the central bore between the shoulder 9 and the lower end of the upper section [0 of the electrode. The coil spring i6 is positioned in this recess and is compressed between the upper edge of the collar l4 and the lower end of the upper section It when the upper section of the electrode is threaded into the insulator.

The space within the recess IT is filled with a mixture of a ceramic cement and a finely ground metal. I prefer to use a chemically setting cement similar to a mixture of talc, water and a silicate of soda having a high soda ratio intermixed with a very finely powdered molybdenum but other materials will function satisfactorily as will be described presently. It will be noted that the cement and metal mixture is squeezed or flows upwardly between the threads H of the upper section of the electrode and the threads 8 on the insulator as indicated at IS in Fig. 3. The mating threads 8 and H are purposely made with a relatively loose fit to permit this flow of cement.

In manufacturing my spark plug I provide the insulator as described and insert the lower section (3 of the electrode downwardly through the central bore preferably with the coil spring positioned around the centering portion I5. I then introduce a predetermined and measured amount of the intermixed cement and molybdenum in the central bore permitting the mixture to come to rest in the recess 11. This is preferably accomplished by using a slender injector tube (not shown) which will discharge the desired amount of the mixture directly into the recess. The upper section 10 of the electrode is then inserted into the bore and screwed into the internal threads 8. The lower end of the upper section in will immediately engage the coil spring [6 and compress the spring against the collar hi on the lower section of the electrode. This will firmly seat the collar on the lower section against the shoulder in the central bore and prevent the escape of any of the seal-. ing mixture into the lower portion of the central bore. This feature is important in that the spacing between the lower section of the electrode and the lower end of the central bore is critical in determining the flash over and fouling characteristics of the spark plug. The lower end of the upper section Ill will then commence to penetrate into the mass of sealing mixture forcing the mixture completely around the coil spring and the upper end of the lower section of the electrode. Further lowering of the upper section it! will displace a portion of the sealing 55 mixture upwardly between the threads 8 and H as previously described, the sealing mixture being introduced in a semi fiuid or plastic state to permit this flow or displacement.

If the charge of sealing mixture has been accurately measured and properly placed in the recess H, a spark plug of the proper operating characteristics results from the above procedure. If, however, through some manufacturing error an improper amount of sealing mixture has been placed in the recess or if the mixture failed to reach the recess, the spark plug will have faulty operating characteristics even though a physical gas-tight seal may be formed around the center electrode so that the usual pressure tests of the spark plug will not reveal the fault. The coil spring 16 will, of course, always form a continuous electrical path through the center electrode so that an electrical test of the spark plug is of little value.

After forming the insulator and center electrode assembly as previously described, I subject the spark plug to a fluoroscopic or other radiographic inspection as indicated in Fig. 4. The radiographic rays of the inspection machine will be completely stopped by the metal bodies of the upper and lower sections of the electrode and the coil spring l6, these parts appearing as a black shadow as shown in Fig. 4 at IS. The body of the insulator will appear as a light gray shadow 20 having a definite line along the sides of the recess I! where the thickness of the insulator is a maximum. The sealing material due to the presence therein of the molybdenum will appear as an intermediate dark gray shadow clearly indicating the presence and location of the sealing material. Fig. 4 represents a faulty spark plug in which the sealing material has by accident collected between the threads as indicated at 2| only a portion of the mixture having entered the recess H as is indicated at 22. This plug would have insufficient heat dissipating area and would consequently overheat in an engine.

I prefer to use molybdenum in the sealing mixture because I have found that molybdenum appears more distinctly in the radiographic inspection of the spark plugs so that a relatively smaller amount is necessary to provide quick and accurate inspection of the spark plugs. However,

other metals such as powdered copper in larger.

quantities may be used in the sealing mixture and other types of sealing mixtures may also be substituted for the cement described. I have found that a mixture of 5% molybdenum renders the location of the sealing mixture apparent on a fluoroscopic examination of the spark plugs but a somewhat larger percentage may be used to reduce the eye strain of the person making the inspection.

I prefer to make the fluoroscopic examination of the spark plug immediately after the upper section l6 of the electrode has been installed in the insulator and before the sealing mixture has set. By doing this it is possible to remove the upper section It of the electrode from faulty plugs and either remove excess sealing material or add more sealing material to correct the fault in the particular spark plug, thus reducing waste in the manufacturing process. However, the examination may be made at any time prior to shipment of the sparks plugs and still obtain the commercial advantage of being able to assure the purchaser of the uniformity and quality of a shipment of spark plugs, all the faulty plugs having been removed and such salvage value as is possible having been obtained from them.

I have described a highly practical commercial design determined largely on the desired heat conducting properties of the spark plug.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A spark plug comprising an insulator defining an internally threaded and upwardly shouldered central bore, a center electrode having a lower section extending from the lower end of said bore and having a collar engaging the shoulder of said bore, an upper section of said electrode extending from the top of said bore and having a threaded portion loosely engaging the threaded portion of said bore, the opposed ends of said sections being spaced apart, a coil spring compressed between and engaging the ends of said sections, and a sealing mixture including finely divided and intermixed cement and powered molybdenum positioned between the ends of said electrode sections and between the threaded portions of said bore and said upper section of said electrode, said mixture including between 4 and 8 percent of molybdenum.

2. A spark plug comprising an insulator defining a shouldered central bore, said bore being of enlarged diameter above the shoulder and having radial grooves formed in the walls thereof above said shoulder, a lower section of a center electrode extending from the bottom of said bore and having a collar engaging said shoulder, an upper section of said center electrode extending from the upper end of said bore and having a collar engaging the end of said insulator to position the inner end of said upper section in spaced relationship with the inner end of said lower section, said upper section having radial projections thereon opposed to said grooves in said bore, a coil spring compressed between the ends of said sections, and a mixture of finely divided and intermixed chemically setting cement and powdered molybdenum positioned in said bore between said sections and between the projections on said upper section and the grooves in said bore, said mixture including between 4 and 8 percent of molybdenum.

3. A spark plug comprising an insulator defining a shouldered central bore, said bore being of enlarged diameter above the shoulder and having radial grooves formed in the walls thereof above said shoulder, a lower section of a center electrode extending from the bottom of said bore and having a collar engaging said shoulder, an upper section of said center electrode extending from the upper end of said bore and having a collar engaging the end of said insulator to position the inner end of said upper section in spaced relationship with the inner end of said lower section, said upper section having radial projections thereon opposed to said grooves in said bore, a coil spring compressed between and engaging the ends of said sections, and a mixture of finely divided and intermixed chemically setting cement and powdered metal positioned in said bore between said sections and between the projections on said upper sections and the grooves in said bore, said mixture including between 4 and 8 percent of metal.

4. The method of manufacturing spark plugs having an insulator with an upwardly shouldered central bore and a sectional center electrode sealed in said bore by a measured amount of chemically setting cement which comprises the steps of mixing finely divided molybdenum with said cement in unset condition and in the proportion of between 4 and 8 per cent of the cement, positioning part of the sections of said electrode in said bore, introducing the mixture of cement and molybdenum into said bore, positioning the remainder of the sections of said electrode in said bore, immediately subjecting the spark plug so assembled to radiographic inspection to determine the accuracy of the location of said cement, and permitting the cement to harden in spark plugs whose radiographic inspection indicates proper location of the cement.

5. The method of manufacturing spark plugs having an insulator with a central bore and a sectional center electrode sealed in said bore by a measured amount of chemically setting cement which comprises the steps of mixing finely divided metal with said cement in the unset condition of the cement and in the proportion of between 4 and 8 per cent of the cement, positioning part of the sections of said electrode in said bore, introducing the mixture of cement and metal into said bore, positioning the remainder of the sections of said electrode in said bore, immediately subjecting the spark plug so assembled to radiographic inspection to determine the accuracy of the location of said cement, and permitting the cement to harden in spark plugs whose radiographic inspection indicates proper location of the cement.

REX J. L. DU'ITERER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,552,622. Leslie Sept. 8, 1925 1,617,758 Heynemann Feb. 15, 1927 2,179,609 Bidwell Nov. 14, 1939 2,248,415 Schwartzwalder et a1. July 8, 1941 2,246,948 McCarty et al. June 24, 1941 2,380,579 Cipriani July 31, 1945 

